Distributed antenna system

ABSTRACT

A technology related to a distributed antenna system is disclosed. In an exemplary embodiment, a distributed antenna system may include a master unit and a plurality of remote units. The master unit may be interfaced with a wireless communications network and perform a bidirectional simultaneous digital radio frequency distribution of a wireless signal. The plurality of remote units may be each coupled to the master unit, and each perform a wireless transmission or reception of a split radio frequency signal to or from terminals located within a coverage. The master unit and the plurality of remote units may transmit or receive digital radio frequency signals in a wavelet transform domain. The master unit may determine whether the digital radio frequency signal, transmitted by each of the remote units, is normal, and merge the digital radio frequency signals.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.16/234,545 (now pending), filed Dec. 27, 2018, which is a continuationof U.S. application Ser. No. 15/091,912 (now U.S. Pat. No. 10,200,157),filed Apr. 6, 2016, which claims the benefit under 35 U.S.C. § 119(a) ofKorean Patent Application No. 10-2015-0154267, filed on Nov. 4, 2015, inthe Korean Intellectual Property Office, the entire disclosure of whichis incorporated herein by reference for all purposes.

BACKGROUND 1. Field

The following description relates to a wireless communicationstechnology, and more specifically, to a technology related to adistributed antenna system.

2. Description of the Related Art

U.S. Pat. No. 7,639,982 discloses a typical distributed antenna systemincluding a digital host unit and digital remote units. Such adistributed antenna system improves reliability and coverage withreduced total power by splitting a radio frequency signal into aplurality of remote units that are spatially separate from each other.An uplink signal, which is transmitted from the plurality of digitalremote units to an uplink, is added in a time domain at a digital hostunit, which is then transmitted to a mobile telecommunications switchingoffice (MTSO).

Since the radio frequency signal is transmitted through an optical fibernetwork, etc. in a time domain, there may be poor transmissionefficiency because of data redundancy, and it may be difficult toanalyze characteristics of individual digital radio frequency signals atdigital remote units.

SUMMARY

The purpose of a proposed invention is to improve transmissionefficiency between node units that composes a distributed antennasystem.

Moreover, the proposed invention is to improve stability in operationsof a distributed antenna system.

Furthermore, the proposed invention is to facilitate determining whethera terminal signal is normal through an economical transform with a smallamount of calculations, without excessively increasing latency.

In one general aspect, a distributed antenna system includes a masterunit and a plurality of remote units. The master unit is interfaced witha wireless communications network and performs a bidirectionalsimultaneous digital radio frequency distribution of a wireless signal.The plurality of remote units is each coupled to the master unit, andeach performs a wireless transmission or reception of a split radiofrequency signal to or from terminals located within a coverage.

The master unit and the plurality of remote units transmit or receivedigital radio frequency signals in a wavelet transform domain.

The master unit may determine whether the digital radio frequencysignal, transmitted by each of the remote units, is normal, and mergethe digital radio frequency signals.

The master unit may determine whether a corresponding split radiofrequency signal is normal based on the digital radio frequency signalstransformed to a wavelet domain.

The master unit may determine whether the digital radio frequencysignal, transmitted by each of the remote units, is normal, andcalculate and merge a weighted sum of each radio frequency signal, ofwhich a weight changes according to whether the digital radio frequencysignal is normal.

The master unit may determine whether each digital radio frequencysignal, transmitted by each of the remote units, is normal, and mergenormal and abnormal digital radio frequency signals into respectivegroups.

The master unit and the plurality of remote units may compress thedigital radio frequency signal, on which a wavelet-transform has beenperformed, and transmit or receive the compressed digital radiofrequency signal.

The distributed antenna system may be coupled to the master unit on oneside thereof and to another plurality of remote units on the other sidethereof, and further comprise a hub unit to relay digital radiofrequency signals in a wavelet transform domain, which are transmittedand received between the plurality of remote units and the master unit.

Other features and aspects may be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a distributed antenna system accordingto an exemplary embodiment.

FIG. 2 is a diagram illustrating the configuration of a master unitaccording to an exemplary embodiment.

FIG. 3 is a diagram illustrating the configuration of a master unitaccording to another exemplary embodiment.

FIG. 4 is a diagram illustrating the configuration of a remote unitaccording to an exemplary embodiment.

FIG. 5 is a diagram illustrating the configuration of a remote unitaccording to another exemplary embodiment.

FIG. 6 is a diagram illustrating the configuration of a remote unitaccording to another exemplary embodiment.

FIG. 7 is a diagram illustrating the configuration of a remote unitaccording to still another exemplary embodiment.

FIG. 8 is a diagram illustrating the configuration of a remote unitaccording to yet another exemplary embodiment.

Throughout the drawings and the detailed description, unless otherwisedescribed, the same drawing reference numerals will be understood torefer to the same elements, features, and structures. The relative sizeand depiction of these elements may be exaggerated for clarity,illustration, and convenience.

DETAILED DESCRIPTION

The following description is provided to assist the reader in gaining acomprehensive understanding of the methods, apparatuses, and/or systemsdescribed herein. Accordingly, various changes, modifications, andequivalents of the methods, apparatuses, and/or systems described hereinwill be suggested to those of ordinary skill in the art. Also,descriptions of well-known functions and constructions may be omittedfor increased clarity and conciseness.

FIG. 1 is a diagram illustrating a distributed antenna system accordingto an exemplary embodiment. As illustrated in FIG. 1, the distributedantenna system according to an exemplary embodiment includes a masterunit 200 and a plurality of remote units 300.

The master unit 200 is interfaced with a wireless communications network100 and performs a bidirectional simultaneous digital radio frequencydistribution of a wireless signal. The wireless communications network100 is a communications node that is to provide the wirelesscommunications through the distributed antenna system, and for example,may be the mobile communications base station. In another example, thewireless communications network 100 may be Ethernet nodes that areconnected to a network backbone.

FIG. 1 illustrates one wireless communications network 100 that isconnected to the master unit 200, but exemplary embodiments thereof arenot limited thereto. For example, a plurality of wireless communicationsnetworks having different standards or frequency bands may be connectedto the master unit 200. Even though the RF band signal of each wirelesscommunications network is added, the added RF band signal may beefficiently separated and extracted by devices, which are located withineach wireless communications, due to the characteristics of the wirelesscommunications itself. An RF adder may be added between the master unit200 and the plurality of wireless communications networks nodes so as tosupport the plurality of wireless communications networks.

The master unit 200 transforms, to a digital radio frequency signal, ananalog radio frequency signal of the RF band that is received from thewireless communications network 100; and then splits the digital radiofrequency signal into a plurality of output ports. FIG. 1 illustratesthe master unit 200, which has, for example, three output ports. In thepresent disclosure, the ‘radio frequency signal’ indicates an electricalsignal inside the distributed antenna system, or may indicate a digitalor analog signal, an RF band signal, an intermediate frequency (IF) bandsignal, and even a baseband signal. The ‘radio frequency signal’ iscalled such a name due to the fact that the distributed antenna systemuses a radio frequency signal, such as a mobile communications, Wi-Fisignal, etc., and that even though such a signal goes through bandconversion by a mixer for the convenience of transmission or processinginside the system thereof, its substance is still such a radio frequencysignal. Accordingly, among these radio frequency signals, the ‘digitalradio frequency signal’ refers to a signal that is transformed todigital.

Remote units 300 may be connected to such output ports. Each of theplurality of remote units 300 is coupled to the master unit 200, andeach performs the wireless transmission or reception of the split radiofrequency signal to or from terminals, which are located within thecoverage. In a case the master unit 200 has the sufficient output portscorresponding to the scale of a system, the remote units 300 may beconfigured to form a star network around the master unit 200. The signalfor the interface between the master unit 200 and the mobilecommunications network 100 may be transmitted through coaxial cables,optical fibers, or the like. For such configuration, generalcommunications components may be added to the master unit 200. Also, oneof the various communications lines, which are appropriate for thecapacity, e.g., coaxial cables, Ethernet cables, optical fibers, betweenthe master unit and the remote unit; the remote unit; the master unitand a hub; and the hub and remote unit, may be applied.

The ‘analog radio frequency signal’ or ‘radio frequency signal’ that hasno additional limit, as described in the present disclosure, indicates asignal of an RF band, which may be transmitted or received through anantenna. A ‘digital radio frequency signal’ indicates a signal, which isacquired after the analog radio frequency signal is band-shifted to alow frequency band and converted to the digital signal. A digital radiofrequency signal in a downlink channel may be a signal, which isacquired after the analog radio frequency signal, received from thewireless communications network 100, is band-shifted to a low frequencyband and converted to the digital. A digital radio frequency signal inan uplink channel may be a signal, which is acquired after the radiofrequency signal, received from terminals within the correspondingcoverage at each remote unit, is band-shifted to a low frequency bandand converted to the digital.

Also, a ‘split digital radio frequency signal’ indicates a signal, whichis acquired after the signal that has been split from a radio frequencysignal of an RF band is band-shifted to a low frequency band andconverted to the digital. Such a split digital radio frequency signalmay be generated from a radio frequency signal of an RF band through asignal process of, at a master unit, being band-shifted to a lowfrequency band and converted to the digital, and at a remote unit, beingfan-out through a fan-out buffer.

In one exemplary embodiment, the master unit 200 and a plurality ofremote units 300 transmit or receive a digital radio frequency signal toor from a wavelet transform domain. The digital radio frequency signalin the wavelet transform domain may have the signal characteristics thatare different from those in the time or frequency domain. For example,in the wavelet transform domain, the digital radio frequency signal maybe more advantageous to compression. In another example, in the wavelettransform domain, the digital radio frequency signal may have anadvantage of reliability or computation in determining its normality.

In another exemplary embodiment, the master unit 200 may determinewhether the digital radio frequency signals transmitted by each of theremote units 300 is normal, and accordingly, may merge the correspondingdigital radio frequency signals. By the incoming abnormal radiofrequency signals, which are generated by a mobile terminal performingan abnormal operation, the communications faults may occur in a lot ofmobile terminals located within the coverage of the corresponding basestation, but may not occur depending on a communications method.

In another exemplary embodiment, the master unit 200 may determinewhether the corresponding split radio frequency signal is normal, basedon the digital radio frequency signal that is transformed to the waveletdomain. Whether the split radio frequency signal of the correspondingremote unit is normal may be determined through the distribution patternor characteristics of the wavelet coefficients of the digital radiofrequency signal.

In still another exemplary embodiment, the master unit 200 may determinewhether the digital radio frequency signal, transmitted by each of theremote units 300, is normal, and calculate and merge the weighted sum ofthe respective digital radio frequency signals, of which the weight maydepend on whether the digital radio frequency signal is normal. If it isassumed that the signal of the weighted sum, generated by the masterunit 200, is y; each digital radio frequency signal is x_(i); the weightcorresponding to x_(i) is a_(i); and the number of the connected remoteunits 300 is N, the signal of the weighted sum may be represented byEquation 1 as shown below.

$\begin{matrix}{y = {\sum\limits_{1}^{N}\;{a_{i} \cdot x_{i}}}} & (1)\end{matrix}$

Here, the weight a_(i) may be determined depending on whether thecorresponding digital radio frequency signal x_(i) is normal. Forexample, the master unit 200 may lower the weight of the abnormalsignals, which leads to the reduction of its importance in the signal ofthe weighted sum, and transmit the lowered weight to an upper node. Inanother example, in a case in which the abnormality degree of theabnormal signals is higher than a certain value, the master unit 200 maynot transmit said signal component to the upper node by setting theweight as 0.

The master unit 200 and the plurality of the remote units 300 maycompress the digital radio frequency signal, on which a wavelettransform has been performed, and transmit or receive the compresseddigital radio frequency signal. For example, the master units and theremote units 300 may transmit only the wavelet coefficients of whichsize are higher than a certain value, thereby performing a linearcompression in a wavelet transform domain.

A distributed antenna system may be coupled to the master unit 200 onone side thereof and to another plurality of remote units on the otherside thereof, and further include a hub unit 500 that relays digitalradio frequency signals in a wavelet transform domain, which aretransmitted and received between the remote units and the master unit.When the master unit 200 needs to be connected to the remote units 300,of which the number is greater than that of the ports the master unit200 has, the distributed antenna system may be provided with a hub unit500, to which the remote units 300 may be connected. The hub unit 500may be connected to the master unit 200 directly or to the cascadedremote units. Since the configuration of such a hub unit 500 iswell-known, the detailed description thereof is omitted here.

FIG. 2 is a diagram illustrating the configuration of a master unitaccording to an exemplary embodiment. As illustrated in FIG. 2, a masterunit 200 according to an exemplary embodiment includes a wavelet signalprocessor 210, a signal splitter 250, a signal combiner 290, and aninverse wavelet signal processor 270. Each of FIG. 2 and the followingdiagrams is shown as a logical functional unit. Each diagram may beshown as one individual component or as a module in which a plurality ofcomponents are assembled. Alternatively, neighboring or separated twoblocks may be physically configured as one component; or a part of saidneighboring or separated two blocks may do. In addition, some of thedescribed functions may be implemented according to a microprocessor andprogram commands. It may be understood that such an implementation maybe variously selected by those skilled in the art.

First, a downlink path will be specifically described. In one exemplaryembodiment, a downlink path of the master unit 200 includes an RFtransceiver 240, a wavelet processor 210, a signal splitter 250, and atransceiver 260. The wavelet processor 210 transforms, to a waveletdomain, a radio frequency signal coming from a mobile communicationsnetwork. In one exemplary embodiment, the wavelet processor 210 includesan RF processor 211 and a wavelet transformer 213. The RF signalprocessor 211 may include a low-noise amplifier; a mixer thatband-shifts a signal to an intermediate frequency (IF) band; and ananalog-to-digital converter that converts such an analog IF signal to adigital signal. The wavelet transformer 213 performs a wavelet transformon the radio frequency signal that has been transformed in the digital,which is then transformed to a serial packet frame appropriate for theserial transmission according to a selected transmission standard.

In one exemplary embodiment, the signal splitter 250 splits, into aplurality of digital radio frequency signals, the digital radiofrequency signal transformed to a wavelet domain as described above,which is then output. The signal splitter 250 may be, for example, afan-out buffer. According to the input terminal properties and thenumber of the ports of the transceiver 260 that is connected to thesignal splitter 250, the fan-out buffer may buffer the appropriateoutput properties.

As illustrated in FIG. 2, the master unit 200 includes an RF transceiver240 additionally. The RF transceiver 240 is a base station interfaceunit (BIU), which is an interface between a base station transceiversystem (BTS) and the master unit 200. Such a BIU, i.e., the RFtransceiver 240, may be equipped separately for each mobilecommunications service provider and for each frequency band. A pluralityof radio frequency signals, connected to the master unit 200, may beprocessed as merged or separated individually at the RF transceiver 240.The RF transceiver 240 transforms a high-power signal, coming from themobile communications network the same as a base station, into the powerthat is appropriate for the process at the master unit 200.

The transceiver 260 having the ports, connected to the plurality ofremote units, may include a plurality of wavelength divisionmultiplexing (WDM) transceiver. In a case where a radio frequency signalis transmitted through a passive optical network (PON) using a WDMmethod, the radio frequency signal may be transmitted or received notonly through one optical fiber line, but also may be transmitted in sucha way that makes the carrier frequency changed and the plurality ofradio frequency signals split. For example, while the plurality of radiofrequency signals of the service providers, coming from the mobilecommunications network, are each processed at the plurality of waveletprocessors 210, which then pass through the signal splitter 250, and areelectrically-optically transformed, the plurality of radio frequencysignals may be modulated into the carrier frequencies different fromeach other, which is then transmitted through the same optical fiberline. In another exemplary embodiment, a radio frequency signal for avoice communications service, and a WI-FI radio frequency signal for awireless internet service are each processed at the plurality of waveletprocessors 210, which then pass through the signal splitter 250, and aremodulated at each port of the transceiver 260 into the carrierfrequencies different from each other, which is then transmitted throughthe same optical fiber line.

Hereinafter, an uplink path will be specifically described. In oneexemplary embodiment, an uplink path of a master unit 200 includes thetransceiver 260, a signal merger 290, an inverse-wavelet signalprocessor 270, and the RF transceiver 240.

The signal merger 290 merges digital radio frequency signals in awavelet domain, which is received from a plurality of remote units. Thepacket streams of the digital radio frequency signals are separated froma frame and synchronized, so that wavelet coefficients corresponding tothe same wavelet basis may be added to and combined with each other. Thesignal merger 290 extracts a payload from a serial packet frame of theplurality of ports of the transceiver 260 according to a selectedtransmission standard. Then, the signal merger 290 transforms such apayload to parallel data and stores the transformed payload in thebuffer of each port. Then, the signal merger 290 synchronizes thebuffered digital radio frequency signals of each port, to which thecorresponding wavelet coefficients are added and merged together,thereby outputting the resultant signal. That is, the digital radiofrequency signal from each remote unit is added in a wavelet transformdomain.

The signals, added in a radio frequency domain, may be separated intoeach signal of the mobile terminals from a base station according to thecorresponding communications method. In addition, since a wavelettransform is a linear transform, each of the radio frequency signals, onwhich a wavelet transform has been performed, is processed transparentlywith regard to the merging in the signal merger 290.

The inverse-wavelet signal processor 270 performs an inverse-wavelettransform on the merged digital radio frequency signal, which is thentransformed to the radio frequency signal and output to a mobilecommunications network. As illustrated in FIG. 2, the inverse-waveletsignal processor 270 includes an inverse-wavelet transformer 273 and aninverse-RF signal processor 271. The terms, such as inverse-waveletsignal processor 270, the inverse-wavelet transformer 273, and theinverse-RF signal processor 271, should not be understood as having thepath configuration that is necessarily inverse to the wavelet signalprocessor 210, the wavelet transformer 213, and the RF signal processor211. The inverse-wavelet transformer 273 performs an inverse-wavelettransform on the digital radio frequency signal that has been merged atthe signal merger 290. The inverse-RF signal processor 271 correspondingto the RF signal processor 211 in the downlink path may include: adigital to analog converter to convert the digital radio frequencysignal, on which the inverse-wavelet transform has been performed, to ananalog signal; a mixer to band-shift the radio frequency signal, whichhas been converted to the analog signal, into the originalhigh-frequency band; and a power amplifier. Intermediate frequenciescoming from the same generator are input to the mixers of the RF signalprocessor 211 and the inverse-RF signal processor 271. The RFtransceiver 240 amplifies and output the additional power that is enoughto be interfaced with the mobile communications network.

The master unit may further include a merge controller 291 thatdetermines whether the digital radio frequency signal, which each remoteunit has transmitted, is normal and accordingly controls the merging inthe signal merger 290.

The merge controller 291 may determine whether the split radio frequencysignal of the corresponding remote unit is normal, based on the digitalradio frequency signal that has been transformed to a wavelet domain. Byanalyzing characteristics, such as a size and a distribution of eachwavelet coefficient, the merge controller 291 may determine whether thesplit radio frequency signal of the corresponding remote unit is normal.In such a case, the remote units do not transmit state information. Onlywhat the master unit does is to determine whether the remote unit isnormal, based on the digital radio frequency signal that has beentransmitted by the remote unit and transformed in a wavelet domain.

The following characteristics are defined: the characteristics of thecoefficients of normal radio frequency signals; a function ofcalculating feature values from the coefficients of the radio frequencysignal (a calculation function); and the feature values of normal radiofrequency signals or the range thereof. The range of the feature valuesof the normal radio frequency signals may be empirically defined. Thefeature value of the received digital radio frequency signal that hasbeen transformed into a wavelet domain is calculated through thecalculation function, and is compared with the stored feature values ofthe normal range so that whether the digital radio frequency signal isnormal may be determined. In another example, the followingcharacteristics are defined: the characteristics of the coefficients ofabnormal radio frequency signals; a function of calculating featurevalues from the coefficients of the radio frequency signal (acalculation function); and the feature values of abnormal radiofrequency signals or the range thereof. The range of the feature valuesof the normal radio frequency signals may be empirically defined. Thefeature value of the received digital radio frequency signal that hasbeen transformed into a wavelet domain is calculated through thecalculation function, and is compared with the stored feature values sothat whether the digital radio frequency signal is normal may bedetermined.

The master unit may determine whether the corresponding digital radiofrequency signal is normal by analyzing the existence of, for example,the digital radio frequency signal's signal power, signal to noise ratio(SNR), voltage standing wave ratio (VSWR), adjacent channel leakageratio (ACLR), spectral emission mask (SEM), passive intermodulation(PIM), spurious signal, etc. The signal power, SNR, VSWR, ACLR, etc. maybe the calculation function.

The merge controller 291 determines whether the digital radio frequencysignal, transmitted by each remote unit, is normal, calculates andmerges a weighted sum of each of the digital radio frequency signals,and determines each weight according to whether the corresponding splitradio frequency signal is normal. Whether the corresponding split radiofrequency signal is normal depends on an analysis result of the digitalradio frequency signal in a wavelet transform domain. The weighted summay be, for example, calculated, as represented by Equation 1. Inresponse to the determination that the digital radio frequency signal isabnormal, the weight is set as ‘0’, and in response of the determinationthat the digital radio frequency signal is normal, the weight is set as‘1’. In addition, in response to the determination that the digitalradio frequency signal is normal, which is, however, a weak signal,amplification coefficients may be set to reach a standard strength onaverage, and in the case of a strong signal, attenuation coefficientsmay be set to reach the standard strength on average.

The merge controller 291 merges and calculates the weighted sum of eachof the digital radio frequency signals, and determines each weightaccording to whether the corresponding split radio frequency signal isnormal. The merge controller 291 may determine whether the digital radiofrequency signal, transmitted by each remote unit, is normal, based onstate information that each remote unit has transmitted. The weightedsum may be calculated, for example, as Equation 1. If it has beendetermined, based on the received state information, that the digitalradio frequency signal is not normal, the weight is set as ‘0’, and inresponse of the determination that the digital radio frequency signal isnormal, the weight is set as ‘1’.

The state information may be generated by analyzing the existence of,for example, the radio frequency signal's signal power, signal to noiseratio (SNR), voltage standing wave ratio (VSWR), adjacent channelleakage ratio (ACLR), spectral emission mask (SEM), passiveintermodulation (PIM), spurious signal, etc. Also, the state informationmay be the radio frequency signal's characteristics information itself,e.g., a power, frequency distribution characteristics, bandcharacteristics, etc. In such a case, the master unit may determine thecorresponding remote unit's radio frequency signal is abnormal not byusing the state information itself but by additionally processing thereceived state information.

In addition, in response to the determination that the radio frequencysignal is normal, which is, however, a weak signal, amplificationcoefficients may be set to reach a standard strength on average, and inthe case of a strong signal, attenuation coefficients may be set toreach the standard strength on average.

The RF signal processor 211 and the inverse-RF signal processor 271 maybe implemented as one RF component. The wavelet transformer 213 and theinverse-wavelet transformer 273 may be implemented by a microprocessor,a digital signal processor, or a series of program modules that areaccordingly executed. Many functions of the signal splitter 250, thesignal merger 290, and the merge controller 291 may be implemented bythe microprocessor, digital signal processor, or the series of theprogram modules that are accordingly executed, which are the same asdescribed above.

FIG. 3 is a diagram illustrating the configuration of a master unitaccording to another exemplary embodiment. As illustrated in FIG. 3, amaster unit according to another exemplary embodiment further includes acompressor 220 and a decompressor 280, compared to the exemplaryembodiment in FIG. 2, which is the difference therebetween. Thecompressor 220 compresses the digital radio frequency signal, which hasbeen transformed to a wavelet domain, between a wavelet signal processor210 and a signal splitter 250. The decompressor 280 decompresses thedigital radio frequency signal in a wavelet domain, which has beenmerged, between a signal merger 290 and an inverse-wavelet signalprocessor 270. Since the signals compressed at each of the remote unitsare merged at the signal merger 290 of a master unit, which is thendecompressed at the decompressor 280, the compression algorithm isrequired to be linear so as to recover the radio frequency signal thathas been received from each remote unit. The compression algorithm maybe, for example, an algorithm that sets coefficients as ‘0’, which aresmaller than a certain size among wavelet coefficients. Reducing thenumber of transmitted coefficients may make the data compressed.

FIG. 4 is a diagram illustrating the configuration of a remote unitaccording to an exemplary embodiment. As illustrated in FIG. 4, a remoteunit 300 according to an exemplary embodiment includes an uppertransceiver 360, an inverse-wavelet signal processor 370, and a waveletsignal processor 310. The remote units according to the exemplaryembodiment illustrated in FIG. 4 may be connected to a plurality ofports of a master unit in the form of a star-shaped network.

First, a downlink path will be specifically described. A downlink pathof the remote unit includes the upper transceiver 360, theinverse-wavelet signal processor 370, and an RF transceiver 340. Theupper transceiver 360 transmits or receives, to or from an upper node, adigital radio frequency signal in a wavelet domain. The uppertransceiver 360 is a wavelength division multiplexing (WDM) transceiver.In a case where the digital radio frequency signal is transmittedthrough a passive optical network (PON) using a WDM method, the digitalradio frequency signal may be transmitted or received not only throughone optical fiber line, but also may be transmitted in such a way thatmakes the carrier frequency changed and the plurality of radio frequencysignals split.

The inverse-wavelet signal processor 370 performs an inverse-wavelettransform on the digital radio frequency signal in a wavelet domain,output from the transceiver, which is then transformed to the splitradio frequency signal and output to an antenna. As illustrated in FIG.4, the inverse-wavelet signal processor 370 includes an inverse-wavelettransformer 373 and an inverse-RF signal processor 371. The terms, suchas inverse-wavelet signal processor 370, the inverse-wavelet transformer373, and the inverse-RF signal processor 371, should not be understoodas having the path configuration that is necessarily inverse to thewavelet signal processor 310, the wavelet transformer 313, and the RFsignal processor 311. The inverse-wavelet transformer 373 performs aninverse-wavelet transform on the digital radio frequency signal that hasbeen merged at the signal merger 290 of the master unit. The inverse-RFsignal processor 371 corresponding to the RF signal processor 211 in thedownlink path may include: a digital to analog converter to convert thedigital radio frequency signal, on which the inverse-wavelet transformhas been performed, to an analog signal; a mixer to band-shift the radiofrequency signal, which has been converted to the analog signal, intothe original high-frequency band; and a power amplifier. The RFtransceiver 340 amplifies and output the additional power that is enoughto be communicated with a mobile terminal. It is clear that the poweramplifier of the inverse-RF signal processor 371 may be combined withthe power amplifier of the RF transceiver 340.

Next, an uplink path will be specifically described. The uplink path ofthe remote unit includes the RF transceiver 340, the wavelet signalprocessor 310, and the upper transceiver 360. The wavelet signalprocessor 310 transforms a radio frequency signal, which has beenreceived from an antenna and then input through the RF transceiver 340,to a wavelet domain, which is then output to the upper transceiver 360.The wavelet signal processor 310 includes an RF signal processor 311 anda wavelet transformer 313. The RF signal processor 311 includes: alow-noise amplifier; a mixer that band-shifts a signal to anintermediate frequency (IF) band; and an analog-to-digital converterthat converts such an analog IF signal to a digital signal. The wavelettransformer 313 performs a wavelet transform on the radio frequencysignal that has been converted to the digital, which is then transformedto a serial packet frame appropriate for the serial transmissionaccording to a selected transmission standard. Intermediate frequenciescoming from the same generator are input to the mixers of the RF signalprocessor 311 and the inverse-RF signal processor 371.

The remote unit may further include a state determiner 393 thatdetermines whether the radio frequency signal, received from theantenna, is normal. However, exemplary embodiments are not limitedthereto; and the remote unit may not include a state determiner, but maytransmit, to an upper layer, the wavelet coefficient that has beentransformed in a wavelet domain, and let a device on the upper layer,such as the master unit, determine the state. Such a difference in asystem configuration may be selected according to the determination of adesign variable in accordance with a cost of the remote units, whichmore exist in a system compared to the master unit, or a system latency,etc.

The remote unit may generate state information by analyzing theexistence of, for example, the received radio frequency signal's signalpower, signal to noise ratio (SNR), voltage standing wave ratio (VSWR),adjacent channel leakage ratio (ACLR), spectral emission mask (SEM),passive intermodulation (PIM), spurious signal, etc. Also, the stateinformation may be the radio frequency signal's characteristicsinformation itself, e.g., a power, frequency distributioncharacteristics, band characteristics, etc. In such a case, the masterunit may determine the corresponding remote unit's radio frequencysignal is abnormal not by using the state information itself but byadditionally processing the received state information.

The state information generated in the state determiner 393 may bemultiplexed with the digital radio frequency signal at the uppertransceiver 360, which is then transmitted. The state informationgenerated at each of the remote units, which are cascaded to each other,is multiplexed with the state information, received from lower remoteunits, at the upper transceiver 360 of each remote unit. If the uppertransceiver 360 is implemented in a WDM-PON, one carrier frequency maybe assigned to the transmission of the state information. The stateinformation generated at each remote unit may be merged into one frameon a time axis, which is then transmitted as one packet. Also, the stateinformation generated at each remote unit may be configured to haveindividual packets that each include identifiers of each remote unit,e.g., an MAC address, and multiplexed on a time axis, which is thentransmitted by one WDM carrier.

The remote unit transmits the state information, which has beendetermined by the state determiner 393, to an upper node, e.g., themaster unit, another remote unit, or a hub unit, through the uppertransceiver 360. The master unit may determine, based on such stateinformation, whether to transmit the radio frequency signal, coming fromthe corresponding remote unit, to a mobile communications network.

The state determiner 393 determines whether the radio frequency signalis normal, based on the radio frequency signal that has been transformedin a wavelet domain.

The following characteristics are defined: the characteristics of thecoefficients of normal radio frequency signals; a function ofcalculating feature values from the coefficients of the radio frequencysignal (a calculation function); and the feature values of normal radiofrequency signals or the range thereof. The range of the feature valuesof the normal radio frequency signals may be empirically defined. Thefeature value of the received digital radio frequency signal that hasbeen transformed into a wavelet domain is calculated through thecalculation function, and is compared with the stored feature values ofthe normal range so that whether the digital radio frequency signal isnormal may be determined. In another example, the followingcharacteristics are defined: the characteristics of the coefficients ofabnormal radio frequency signals; a function of calculating featurevalues from the coefficients of the radio frequency signal (acalculation function); and the feature values of abnormal radiofrequency signals or the range thereof. The range of the feature valuesof the normal radio frequency signals may be empirically defined. Thefeature value of the received digital radio frequency signal that hasbeen transformed into a wavelet domain is calculated through thecalculation function, and is compared with the stored feature values sothat whether the digital radio frequency signal is normal may bedetermined.

The remote unit may determine whether the corresponding digital radiofrequency signal is normal by analyzing the existence of, for example,the digital radio frequency signal's signal power, signal to noise ratio(SNR), voltage standing wave ratio (VSWR), adjacent channel leakageratio (ACLR), spectral emission mask (SEM), passive intermodulation(PIM), spurious signal, etc. The signal power, SNR, VSWR, ACLR, etc. maybe the calculation function.

As illustrated in FIG. 4, the state determiner 393 has been described asa part of the remote unit 300, but may be implemented as an individualdevice or a computer system outside the remote unit 300.

The RF signal processor 311 and the inverse-RF signal processor 371 maybe implemented as one RF component. The wavelet transformer 313 and theinverse-wavelet transformer 373 may be implemented by a microprocessor,a digital signal processor, a series of program modules that areaccordingly executed, a gate array, or an application specificintegrated circuit (ASIC). Many functions of the state determiner 393may be implemented by the microprocessor, the digital signal processor,and the series of program modules that are accordingly executed, whichare the same as described above. Such a design method of a digitalsystem may be variously selected by those skilled in the art through thepresent technology.

FIG. 5 is a diagram illustrating the configuration of a remote unitaccording to another exemplary embodiment. As illustrated in FIG. 5, aremote unit 300′ further includes a compressor 320 and a decompressor380, compared to the exemplary embodiment in FIG. 4, which is thedifference therebetween. On a downlink path, the decompressor 380decompresses a digital radio frequency signal in a wavelet domain, whichhas been received, between a transceiver 360 and an inverse-waveletsignal processor 370. On an uplink path, the compressor 320 compresses adigital radio frequency signal, which has been transformed to a waveletdomain, between a wavelet signal processor 310 and a transceiver 360. Asdescribed before, a compression algorithm is required to be selectedlinearly with respect to an addition operation.

As illustrated in FIG. 5, a state determiner 393 is a radio frequencysignal that remote units have transmitted and determines whether theradio frequency signal is normal, based on the signal that is before thecompression. However, exemplary embodiments are not limited thereto; andthe remote unit may not include a state determiner 393, but maytransmit, to an upper layer, the wavelet coefficient that has beentransformed in a wavelet domain, and let a device on the upper layer,such as the master unit, determine the state. Such a difference in asystem configuration may be selected according to the determination of adesign variable in accordance with a cost of the remote units, whichmore exist in a system compared to the master unit, or a system latency,etc. Also, in FIG. 5, similar to the above-mentioned exemplaryembodiments, the state determiner 393 determines whether the radiofrequency signal is normal, based on the radio frequency signal that hasbeen transformed in a wavelet domain.

FIG. 6 is a diagram illustrating the configuration of a remote unitaccording to another exemplary embodiment. As illustrated in FIG. 6, adistributed antenna system 300″ further includes a lower transceiver 260and a signal splitter 350.

The lower transceiver 260 outputs a digital radio frequency signal in awavelet domain, which is received from a lower node, to an uppertransceiver 360, and a digital radio frequency signal in a waveletdomain, which is received from an upper node, to a lower node. Remoteunits may be cascaded the same as illustrated in FIG. 1.

The signal splitter 350 splits the digital radio frequency signal in awavelet domain, received from the upper transceiver 360, into aninverse-wavelet signal processor 370 and the lower transceiver 260.

The upper transceiver 360 multiplexes the digital radio frequencysignals in a wavelet domain, each received from the lower transceiver260 and the wavelet signal processor 310, which are then transmitted toan upper node. Here, multiplexing indicates that the radio frequencysignal is not added at a level of an RF signal but transmitted in a formthat is split into an individual RF signal. For example, the uppertransceiver 260 employs a passive optical network (PON) using awavelength division multiplexing (WDM) modulation, the digital radiofrequency signals from the wavelet signal processor 310 and the lowertransceiver 260 are, respectively, modulated to carrier frequencies thatare different from each other, which is then each transmitted to anupper node. The upper node, e.g., a master node, receives the signal,which has been acquired after multiplexing the digital radio frequencysignal, from a plurality of lower nodes through one port. The masterunit may multiplex the received digital radio frequency signals, comingfrom the remote units, differently according to state information, i.e.,whether the signal is normal, and transmit the multiplexed signal to awireless communications network. For example, if it has been determinedthat the signal is abnormal, the master unit may transmit the normalsignal to the upper node except the abnormal signal. In addition, if ithas been determined that the signal is normal, the signal may beattenuated or amplified according to the strength of the signal, whichmay be then multiplexed.

The remote unit may further include a state determiner 393 thatdetermines whether the radio frequency signal, received from an antenna,is normal. The remote unit transmits the state information, which hasbeen determined at the state determiner 393, to an upper node, e.g., amaster unit, another remote unit, or a hub unit, through the uppertransceiver 360. The master unit may determine, based on such stateinformation, whether to transmit the radio frequency signal, coming fromthe corresponding remote unit, to a mobile communications network.

In FIG. 6, similar to the above-mentioned exemplary embodiments, thestate determiner 393 may determine whether the radio frequency signal isnormal, based on the radio frequency signal that has been transformed ina wavelet domain.

However, exemplary embodiments are not limited thereto; and the remoteunit may not include a state determiner, but may multiplex only thewavelet coefficient, transformed in a wavelet domain, for each signal,which is then transmitted to an upper layer, and let a device on theupper layer, such as the master unit, determine the state. Such adifference in a system configuration may be selected according to thedetermination of a design variable in accordance with a cost of theremote units, which more exist in a system compared to the master unit,or a system latency, etc. For example, a remote unit existing at the endof a system may not determine the state but transmits the waveletcoefficient of itself to an uplink, and a remote unit relaying signalsmay generate state information and multiplex a plurality of digitalradio frequency signals according to the state information.

FIG. 7 is a diagram illustrating the configuration of a remote unitaccording to still another exemplary embodiment. As illustrated in FIG.7, a remote unit 300′″ further includes a lower transceiver 260, asignal splitter 350, and a signal merger 390.

The lower transceiver 260 transmits or receives, to or from a lowernode, a digital radio frequency signal in a wavelet domain. The remoteunits may be cascaded through the lower transceiver 260, as illustratedin FIG. 1. A signal splitter 350 splits the digital radio frequencysignal in a wavelet domain, received from an upper transceiver 360, intoan inverse-wavelet signal processor 370 and the lower transceiver 260.

The signal merger 390 merges digital radio frequency signals in awavelet domain, output from a wavelet signal processor 310 and the lowertransceiver 260, which is then output to the upper transceiver 360. Forexample, the merge of the digital radio frequency signals may beperformed through the addition between corresponding coefficients in awavelet domain.

The remote unit may further include a state determiner 393 thatdetermines whether the radio frequency signal is normal, which has beenreceived from an antenna. The remote unit transmits the stateinformation, which has been determined by the state determiner 393, toan upper node, e.g., a master unit, another remote unit, or a hub unit,through the upper transceiver 360. The master unit may determine, basedon such state information, whether to transmit the radio frequencysignal, coming from the corresponding remote unit, to a mobilecommunications network.

Similar to the above-mentioned exemplary embodiments, the statedeterminer 393 determines whether the radio frequency signal is normal,based on the radio frequency signal that has been transformed in awavelet domain.

However, exemplary embodiments are not limited thereto; and the remoteunit may not include a state determiner 393, but may transmit, to anupper layer, the wavelet coefficient that has been transformed in awavelet domain, and let a device on the upper layer, such as the masterunit, determine the state. Such a difference in a system configurationmay be selected according to the determination of a design variable inaccordance with a cost of the remote units, which more exist in a systemcompared to the master unit, or a system latency, etc. For example, aremote unit existing at the end of a system may not determine the statebut transmits the wavelet coefficient of itself to an uplink, and aremote unit relaying signals may generate state information and merge aplurality of digital radio frequency signals according to the stateinformation.

FIG. 8 is a diagram illustrating the configuration of a remote unitaccording to yet another exemplary embodiment. As illustrated in FIG. 8,a remote unit according to another exemplary embodiment further includesa compressor 320 and a decompressor 380, compared to the exemplaryembodiment in FIG. 7, which is the difference therebetween. On adownlink path, the decompressor 380 decompresses the digital radiofrequency signal in a wavelet domain, which has been merged, between asignal splitter 350 and a wavelet signal processor 310. On an uplinkpath, the compressor 320 compresses the digital radio frequency signal,which has been transformed to a wavelet domain, between the waveletsignal processor 310 and a signal merger 390.

A distributed antenna system, described herein, may improve transmissionefficiency between node units that are included therein. In addition,the distributed antenna system may ease an analysis of the individualcharacteristics of a digital radio frequency signal in digital remoteunits, which results in an improvement of stability in operating thedistributed antenna system. Moreover, a signal latency may occur due toa latency that has been already generated at optical fibers, but byusing a wavelet transform that makes less calculation amount andreal-time process possible, the distributed antenna system may determinewhether a terminal signal or a base station signal is normal through aneconomical transform making a small amount of calculations without anexcessive increase in latency.

A number of examples have been described above. Nevertheless, it shouldbe understood that various modifications may be made. For example,suitable results may be achieved if the described techniques areperformed in a different order and/or if components in a describedsystem, architecture, device, or circuit are combined in a differentmanner and/or replaced or supplemented by other components or theirequivalents. Accordingly, other implementations are within the scope ofthe following claims.

What is claimed is:
 1. A communication method, comprising: receiving, bya master station, a first plurality of digital radio frequency signalsfrom a plurality of remote stations, wherein the first plurality ofdigital radio frequency signals are transmitted in a wavelet domain;determining, by the master station, whether each of the first pluralityof digital radio frequency signals is normal or abnormal based on atleast one characteristic of the respective first plurality of digitalradio signals; merging, by the master station, the first plurality ofdigital radio frequency signals to generate a second radio frequencysignal based on the determination on whether the respective firstplurality of digital radio frequency signals is normal or abnormal;inverse-wavelet transforming, by the master station, the second digitalradio frequency signal to generate a third digital radio frequencysignal; and transmitting, by the master station, the third radiofrequency signal to a mobile communication network.
 2. A method of claim1, further comprising: receiving, by the master station, a fourthdigital radio frequency signal from the mobile communication network;transforming, by the master station, the fourth digital radio frequencysignal to the wavelet domain to generate a fifth digital radio frequencysignal; splitting, by the master station, the fifth digital radiofrequency signal into a sixth plurality of digital radio frequencysignals; and transmitting, by the master station, the sixth plurality ofdigital radio frequency signals to the plurality of remote stations. 3.The method of claim 1, wherein merging the first plurality of digitalradio frequency signals to generate the second digital radio frequencysignal comprises: calculating a weight for each of the first pluralityof digital radio frequency signals based on the determination whetherthe respective first plurality of digital radio frequency signals isnormal or abnormal; generating weighted plurality of digital radiofrequency signals based on the respective weight and the correspondingfirst plurality of digital radio frequency signals; and summing theweighted plurality of digital radio frequency signals to generate thesecond digital radio frequency signal.
 4. The method of claim 3, whereinmerging the first plurality of digital radio frequency signals togenerate the second digital radio frequency signal further comprises:grouping the first plurality of digital radio frequency signals into afirst group comprising digital radio frequency signals determined asnormal and a second group comprising digital radio frequency signalsdetermined as abnormal.
 5. The method of claim 3, further comprising:selecting a group of digital radio frequency signals based on therespective weight of the corresponding first plurality of digital radiofrequency signals.
 6. The method of claim 1, further comprising: aftermerging the first plurality of digital radio frequency signals,decompressing the merged first plurality of digital radio frequencysignals to generate the second digital radio frequency signal.
 7. Themethod of claim 2, further comprising: after transforming the fourthdigital radio frequency signal to the wavelet domain, compressing thetransformed fourth digital radio frequency signal to generate the fifthdigital radio frequency signal.
 8. A communication apparatus,comprising: a processor, a memory which stores program instructions,wherein the processor, when executing the program instructions stored inthe memory, is configured to: cause the communication apparatus toreceive a first plurality of digital radio frequency signals from aplurality of remote stations, wherein the first plurality of digitalradio frequency signals are transmitted in a wavelet domain; cause thecommunication apparatus to determine whether each of the first pluralityof digital radio frequency signals is normal or abnormal based on atleast one characteristic of the respective first plurality of digitalradio signals; cause the communication apparatus to merge the firstplurality of digital radio frequency signals to generate a second radiofrequency signal based on the determination on whether the respectivefirst plurality of digital radio frequency signals is normal orabnormal; cause the communication apparatus to inverse-wavelet transformthe second digital radio frequency signal to generate a third digitalradio frequency signal; and cause the communication apparatus totransmit the third radio frequency signal to a mobile communicationnetwork.
 9. The communication apparatus of claim 8, wherein theprocessor is further configured to: cause communication apparatus toreceive a fourth digital radio frequency signal from the mobilecommunication network; cause communication apparatus to transform thefourth digital radio frequency signal to a wavelet domain to generate afifth digital radio frequency signal; cause communication apparatus tosplit the fifth digital radio frequency signal into a sixth plurality ofdigital radio frequency signals; and cause communication apparatus totransmit the sixth plurality of digital radio frequency signals to theplurality of remote stations.
 10. The method communication apparatus ofclaim 8, wherein the processor is further configured to, in merging thefirst plurality of digital radio frequency signals to generate thesecond digital radio frequency signal: calculate a weight for each ofthe first plurality of digital radio frequency signals based on thedetermination whether the respective first plurality of digital radiofrequency signals is normal or abnormal; cause the communicationapparatus to generate weighted plurality of digital radio frequencysignals based on the respective weight and the corresponding firstplurality of digital radio frequency signals; and cause thecommunication apparatus to generate the second digital radio frequencysignal by summing the weighted plurality of digital radio frequencysignals.
 11. The communication apparatus of claim 9, wherein theprocessor is further configured to, in merging the first plurality ofdigital radio frequency signals to generate the second digital radiofrequency signal: cause the communication apparatus to group the firstplurality of digital radio frequency signals into a first groupcomprising digital radio frequency signals determined as normal and asecond group comprising digital radio frequency signals determined asabnormal.
 12. The communication apparatus of claim 11, wherein theprocessor is further configured to: cause the communication apparatus toselect a third group of digital radio frequency signals based on therespective weight of the corresponding first plurality of digital radiofrequency signals.
 13. The communication apparatus of claim 8, whereinthe processor is further configured to: cause the communicationapparatus to, after merging the first plurality of digital radiofrequency signals, decompress the merged first plurality of digitalradio frequency signals to generate the second digital radio frequencysignal.
 14. The communication apparatus of claim 9, wherein theprocessor is further configured to: cause the communication apparatusto, after transforming the fourth digital radio frequency signal to thewavelet domain, compress the transformed fourth digital radio frequencysignal to generate the fifth digital radio frequency signal.